How greatly do exit options vary by region/vault ranking?To shoot for the best exit options is it credited to just shoot for highest ranked firm rather than a lower ranked one where you might like the location better (think starting at NYC V50 or V20 vs Texas biglaw or a smaller region)?

The only exit options that will care about your firm will do so indirectly like being a client and you build a relationship. For non client exit ops, head hunters don't give a fuck and its gonna be more about your experience and what you've actually done. But if you insist on picking a sweatshop so be it.